The present invention relates to an installation for laser welding at least two overlapping metal parts, comprising a laser source, a head for focusing, in the zone of overlap, a laser beam emitted by the source, a mechanism for pressing on a first of the parts and intended to co-operate with means for retaining another part so as to hold the parts that are to be welded pressed together in the region of their zone of overlap, and means for the relative displacement of the head with respect to the zone of overlap of the parts that are to be welded.
The invention applies in particular to the transparency-welding of external body skin panels made of steel sheet for railway vehicles.
Laser transparency-welding allows metal parts to be welded together at their surfaces that face one another in a zone of overlap.
To form a weld between these opposing surfaces in this zone where they are inaccessible, the laser beam impinging on one of the parts passes right through this part and melts the other part. The molten metal solidifies after the laser beam has passed, to form a welded seam.
The use of this transparency-welding technique requires the clearance between the opposing surfaces of the parts that are to be welded to be less than 10% of the total thickness of the zone of overlap.
This constraint on the clearance poses problems in applying this welding technique to railway vehicle exterior body skin panels because of the long lengths over which they need to be welded, it being possible for these lengths typically to be as much as 30 m.
In other fields and for small parts, uniformly spaced rams which clamp the two parts together along the entire length to be welded of the zone of overlap are used in order to comply with this constraint on clearance.
However, this solution would be particularly expensive for welding parts together over relatively long lengths, because of the proliferation in the number of rams.